Method of making a heat exchanger



Dec. 1, 1959 A. B. MODINE METHOD OF MAKING A mm EXCHANGER Filed Nov. 25, 1955 fnverzl or" Griz/4:015: mil-7w 4Q- and described and wind? S ate P Q s Claimsf (era-151.3;

The invention relatesgenerally to heat exchange structures and more particularly to a fin structure ofvariable :thickness and the method of making'the same. I

The advantages of a taperedfin structurein heat ex- *-changers are well known and in certain cases such types f fin structures have been utilized, such constructions, Zhowever, involvingeither an integral preformed construcition, as for example, a coating or a fabricated construction involving aplurality of assembled elements, as for example, that illustrated -in my prior Patent No. 2,339,28 dated January 18, 1944. a

The present inventionis of particular advantage where the fin members are normally formed from sheet material and operatively associated in heat .transfer relationwith one or more fluid conducting elements, a typical example of which is the tubular type automotive radiatorcore having a plurality of parallel fluid conducting tubes con-' Patented Dec. 1, 1959 Fig. l is an enlarged transverse sectional view of a v Fig. 2 may be fabricated;

nected by a plurality of generally parallel fin members formed from sheet or strip material and extending transversely to the tubes. Fin elements of this type have utilized sheet material of substantially uniform thickness and obviously in such case, the thickness of the material is primarily controlled bythat portion of the structure which would require the greatest thickness. In the example of a radiatorcore, that portion would be adjacent the fluid conducting tubes and may involve consideration .of both structural and heat transfer characteristics. Obviously, where a fin structure of'uniform thickness is employeitheentire structure is of necessity the .mum th-ickness required in any portion thereof with Lacorresponding increase in weight, cost of materials, etc.,

overwhat would be required if the unnecessary'material I could be eliminated. 1 4 h The present invention has among its objects the production ofa heat transfer structure which utilizes a sheet metal fin' elementof varying thickness, whereby the various portions of the: fin element may be of substantially minimum thickness consistent with the operational and functional requirements of such portions.

1 "Another object of the invention is the production of such a finelementwvhich may be readily substituted for prior fin structures whereby the fabrication of such exchangers may employ standard techniques and machinery,

etc.

; A further object of the invention is the utilization of a novel, method forming such fin elements whereby the same may be fabricated from stock of either greater or lesser thickness than the maximum thickness of the formed fin element.- 1

Many other objects and advantages of the construction herein shown and described will be obvious to those 3 skilled in the. art from the disclosure herein given.

To this end my invention consists in the novel construcv appended claims; 1

In the 'drawingsfwherein like reference characters indip p catle like or corresponding parts Fig. 4 is an enlarged view similar to Fig. 2 of a fin element formed from. stock of lesser thickness; and

Fig. 5 illustrates a novel way in which the element of Fig. 4 maybe fabricated.

Referring to the drawings, and particularly Figs. 1, 2 and 3, Fig. 1 illustrates a small portion of a tubular type heat exchange structure, portions of two tubes 1 being illustrated, with the tubes 1 being connected by a plurality of fin elements indicated generally by the numeral 2 and formed from sheet material. In the particular example illustrated, the elements 2 are provided with a'plurality of openings 3 through which the respective tubes'extend, which openings 3 are defined by flanges '4 struck from the material of the strip originally positioned at the openings 3, forming annular collars which in theexample illustrated also may function as spacing. means for the strips 2. The portions of the strips 2 intermediate the tubes 1 forming the secondary surface of the heat exchange structure vary in thickness from the central portion 5 thereof to the portions 6 adjacent the respective tubes, the thickness suitably increasing from the intermediate portion 5 tothe portions 6, thus in effect forming fin'structures tapering outwardly with re structure for the particular operational characteristics and'efficiency, as distinguished from prior constructions wherein the fin structures are of substantially uniform thickness, necessitating the utilization of stock having a thickness equal to the maximum required, which in the example given would be the portion 6 adjacent the tubes 1.

, Referring to Fig. 2, y represents the distance from the center line of the tube 1 to the beginning of the tapering portion represented by the letter x, so that the portions 6 have a length of 2y, while the intermediate portionstaper from the thickness of the portions y to approximately one-half thereof in a distance equal to onehalf of x. The construction illustrated in Fig. 2 may be fabricated in the manner illustrated in Fig. 3 wherein the strip 2 is fed between two rollers 7 and 8, the roller 7 beingcylindrical in cross section, while the roller 8 is substantially polygonal in cross section, having a series of sides 9 which are substantially fiat and intersect to form apexes 11. As the rolls 7 and 8 are rotated in the directions indicated by the arrows in Fig. 3, the strip 2 will be formed to substantially the shape illustrated in Fig. 2, and if desired by suitably shaping the roll 8 the exact shape of Fig. 2 could be achieved.

Theaction of the rolls 7 and #8 will result in an increase in the length of the strip and thus the weight per fixed length of the formed strip will be correspondingly reduced to that of the original strip. These results can be readily established mathematically, for example, assuming the center line distance between the tubes -'1 was .5625 inch, the distance y .06 inch and the average thickness of the portion '6 and that of the unformed strip 2 to be .005 inch, with the intermediate portion 5 of minimum thickness being .0( )25 inch, the length of the formed strip would be approximately 25% greater than the original total length of the unformed strip. Likewise there may be areduction in weight in the neighborhood of 20% per fin strip across the exchanger. It will be appreciated that in present day heat exchange design, wherein minimum weight factors are stressed, a saving in weight of the above amount may be a very important design factor, particularly when no loss in efliciency accompanies the weight reduction. As the flanges 4 are formed from the thicker portion *6, a very eflicient heat transfer is effected betwen the fin structure and the tube, as well as providing a stronger and more durable as sembly. Likewise, the working of the metal tends to provide improved engagement between the tubes and fins.

In fabricating the fin structure in the manner illustratedin Fig. 3, the maximum distance or space between the rolls 7 and 8 would normally be somewhat less than the minimum thickness of the original strip in accordance with commercial tolerances to insure a uniformproduct. Figs. 4 and 5 illustrate the method of forming the fin material by means of a pair of rolls the axes of which extend parallel to the longitudinal axis of the strip, the roller 7 being cylindrical, with the roller '8' having a longitudinal sectional shape corresponding to the shape of the top surface of the formed fin as illustrated in Figs. '1, 2, and 3. With this method, the strip S may be of lesser thickness than the formed thickness of the portions 6 and greater than the minimum thickness of the intermediate portion 5 of the formed strip. Thus the roll 8' isprovided with spaced cylindrical portions 12 of minimum diameter corresponding in axial Width to the width of the portions 6 of the fin structure, having intersecting conical portions 13 extending therefrom, the portions 13 increasing in diameter from the portions 12 with adjacent portions 13 intersecting on a circumferential line 14 corresponding to the intermediate portion 5 p of the least thickness of the fin structure.

It is believed apparent from the above description that an equivalent fin structure is provided by either of the methods illustrated in Fig. 3 orS, the main distinction between the two being that in the former the metal is stretched and the area thereby increased, whereas in the latter the material is transferred by pressure from an area of minimum thickness to the area of maximum thickness.

It will be-noted from the above description that I have disclosed a fin structure which may be formed from strip or sheet material and formed by a novel method to provide a tapered fin effect together with improved characteristics and with a corresponding reduction in weight and cost of material of a heat exchanger utilizing the same. It will be particularly noted that the fin structure may be fabricated by a comparatively simple yet highly eflicient method of forming the fin elements.

Having thus described my invention, it is obvious that various immaterial modifications may be made in the same without departing from the spirit of my invention; hence, I do not wish to be understood as limiting myself to the exact form, construction, arrangement and combination of parts herein shown and described, or uses mentioned.

What I claimas new'and desire to secure by Letters Patent is:

1. The method'of forming a heat exchanger including a secondary surface heat exchange element, which cornprises thefollowing steps: subjecting thin flat sheet metal stock of predetermined substantially uniform thickness to forming pressure distributed over a sheet face in a pre determined pattern of non-uniform pressures between op- 'posite faces of said element to effect a flowing of metal from certain areas to laterally adjacent areas to produce an element of a heat exchanger providing integrallyconnected relatively thick portions at longitudinally spaced points and relatively thin portions intermediate said points,

punching'flanged openings in the relatively thick portions for operatively connecting primary tubular heat exchange elements within the flanged openings at the thick portions,

and said relatively thin portions providing finstructures tapering outwardly with respect to the contiguous primary tubular heat exchange elements.

2. The method of forming a secondary surface heat exchange element for a heat exchanger, which comprises the steps: subjecting thin flat sheet metal stock of a predetermined thickness to forming pressures distributed over a face of the sheet in a predetermined pattern of nonuniformpressures between opposite faces of said element to effect a flowing of metal from longitudinally spaced portions which are thereby reduced in thickness providing thin portions, to adjacent intermediate'portions which are thereby increased in thickness providing thick portions, as a resultofsuch forming action, each of such portions extending substantially from one edge of the sheet to the opposite edge thereof, the length of the 7 element remaining substantially constant during the forming action, punching flanged openings in the relatively thick portions for operatively connecting primary tubular heat exchange elements at the relatively thick portions, and said relatively thin portions providing fin structures tapering outwardly with respect to the contiguous flanged openings in the thick portions.

3. .The method of forming a heat exchanger including a secondary surface heat exchange element, which comprises the steps: subjecting thin flat sheet metal stock of substantially uniform thickness to forming pressures resulting from engagement of said stock with a forming element having a non-planar sheet-engaging surface whereby the forming pressures are-distributed across the face of the sheet in a predetermined pattern of nonuniform pressures along said element to efiect a flowing -of metal from certain elongated areas to adjacent substantially parallel extending areas to produce an element of alheat exchanger having relatively thick portions at points to beoperatively connected to primary tubular heat exchange elements and relatively thin portions intermediate such points with such portions being disposed in generally parallel relation, forming flanged openings in the relatively thick portions for operatively connecting across a face of said sheet in .a predetermined pattern of non-uniform pressures on said element to effect a compression of said metal and a longitudinal flowing thereof from certain areas to longitudinally adjacent areas to produce an element of a heatexchanger having alternate relatively thick and thin portions, each of which extends substantially from one edge of the element to the opposite edge thereof with relatively thick portions at points to be operatively connected to primary tubular heat exchange elements and relatively thin portions intermediate -such points, the longitudinal length of the element-being extended as a result of such forming action,

punching flanged openings in the relatively thick portions for operatively connecting the primary tubular heat exchange elements, and said relatively thin portions providing fin structures taperingoutwardly with respect to therelatively thick portions providing a maximum heat transfer with a minimum of metal in the secondary surface. heat exchange element.

5. The method offorming a secondary surface heat exchange-element of a heat exchanger, which comprises .the stepsasubjecting thin flat sheetmetal stock of predetermined thickness to forming pressures of a pair of cooperable spaced-rolls havingaparallel axes, at least one of which varies in diameter along its axis whereby such forming pressures are distributed across a face of the sheet in a predetermined patternof non-uniform pressures between opposed faces of said element to elfect References Cited in the file of this patent a flowing of metal from portions spaced in an axial TED STATES PATENTS direction which are thereby reduced in thickness pro- UNI viding relatively thin portions, to adjacent substantially 529,551 Hollmgsworth 1894 paral-lelly extending intermediate portions which are 5 1,343,753 Sloper June 15, 1920 thereby increased in thickness providing relatively thick 1,313,727 Ludwig Aug. 11, 1931 portions for increasing the strength of said heat ex- 1,929,356 Janitzky Oct 3, 1933 change element, as a result of such forming action, the 4 T 1 J 19 1934 length of the element remaining substantially constant f or une during the forming action forming flanged openings in 10 1,989,796 Firth Feb. 5, 1935 said relatively thick portions for atfixing primary heat 2,023,827 wallman et a1 Dec. 10, 1935 exchange elernents thereto heat exchange relationship, 2,193,231 Gibbons Mar. 12, 1940 and said relatively thm portions providlng fin structures 2,250,542 Lodge July 29 1941 tapering outwardly with respect to the relatively thick portions increasing the heat conductivity of said secondary 15 2,320,500 Ashby June 1943 surface heat exchange element. 2,602,650 Marcotte July 8, 1952 

